Semiconductor device and fabrication method of the semiconductor device

ABSTRACT

A semiconductor device and a fabrication method of the semiconductor device, the semiconductor device including: a substrate; a nitride based compound semiconductor layer placed on the substrate and doped with a first transition metal atom; an aluminum gallium nitride layer (Al x Ga 1−x N) (where 0.1&lt;=x&lt;=1) placed on the nitride based compound semiconductor layer; a nitride based compound semiconductor layer placed on the aluminum gallium nitride layer (Al x Ga 1−x N) (where 0.1&lt;=x&lt;=1) and doped with a second transition metal atom; an aluminum gallium nitride layer (Al y Ga 1−y N) (where 0.1&lt;=y&lt;=1) placed on the nitride based compound semiconductor layer doped with the second transition metal atom; and a gate electrode, a source electrode, and a drain electrode which are placed on the aluminum gallium nitride layer (Al y Ga 1−y N) (where 0.1&lt;=y&lt;=1). Accordingly, piezo charge is inactivated, leakage current and current collapse are reduced, high frequency characteristics can be improved by obtaining a high resistivity semiconductor layer, and stable high frequency performance can be obtained.

CROSS REFERENCE TO RELATED APPLICATION AND INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. P2008-013720 filed on Jan. 24,2008, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and afabrication method of the semiconductor device. In particular, thepresent invention relates to a GaN (gallium nitride) related high powersemiconductor device for obtaining stabilized high frequencyperformance, and a fabrication method of the semiconductor device.

2. Description of the Related Art

It is known that FETs (Field Effect Transistors) using a GaN (galliumnitride) related semiconductor have a large amount of current collapseand have a large amount of leakage current. As one of the cause, crystaldislocations and crystal defects in an epitaxial crystal are mentioned.

Since the crystal defect causes fundamental performance degradation,such as an amount of increase of the leakage current and occurring ofthe current collapse phenomenon, it is dramatically important to obtainan epitaxial layer with little crystal defects.

In order to suppress the amount of crystal dislocations and the amountof crystal defects, a method of inserting an AlGaN (aluminum galliumnitride) layer and an AlN (aluminum nitride) layer into the GaN layer isknown.

As shown in FIG. 1, a conventional semiconductor device includes, forexample, a substrate 10 composed of SiC, a GaN layer 120 placed on thesubstrate 10, an AlN layer or an AlGaN layer 16 placed on the GaN layer120, a GaN layer 200 placed on the AlN layer or the AlGaN layer 16, aAlGaN layer 22 placed on the GaN layer 200, and a gate electrode 26, asource electrode 24, and a drain electrode 28 which are placed on theAlGaN layer 22.

However, since GaN and AlGaN or AlN have a large amount of latticeconstant difference, the amount of electric charges is induced betweenthe GaN layer and the AlGaN layer by piezo polarization effect.Therefore, there was a problem that the amount of electric chargesinduced in the GaN layer degrades the high frequency performance of thesemiconductor device extremely.

For example, in FIG. 1, since the GaN layer 120 and the AlN layer orAlGaN layer 16 have a large amount of lattice constant difference, theamount of electric charges is induced between the GaN layer 120 and theAlN layer or the AlGaN layer 16 by piezo polarization effect. Therefore,there is a problem that the amount of electric charges induced in theGaN layer 120 degrades the high frequency characteristics of thesemiconductor device extremely. Similarly, since the GaN layer 200 andthe AlN layer or AlGaN layer 16 have a large amount of lattice constantdifference, the amount of electric charges is induced between the GaNlayer 200 and the AlN layer or AlGaN layer 16 by piezo polarizationeffect. Therefore, there is a problem that the amount of electriccharges induced in the GaN layer 200 degrades the high frequencycharacteristics of a semiconductor device extremely.

The amount of electric charges induced by such piezo polarization effectbecomes the cause of increasing the conductivity of the GaN layer 120 or200, increasing the leakage current between the gate electrode 26 andthe source electrode 24 or between the gate electrode 26 and the drainelectrodes 28, and reducing power amplification gain of thesemiconductor device.

It is already disclosed about a field effect transistor using a GaNrelated semiconductor which can form a gate size in 0.1 micrometer classand does not occurs the leakage current between the gate electrode andthe source electrode, or between the gate electrode and draininter-electrode, and a fabrication method of the field effect transistor(for example, refer to Patent Document 1). In the Patent Document 1,gate leakage current is reduced by using a field effect transistor whichhas a gate electrode whose sectional shape is T shape.

Moreover, it is already disclosed about a high resistivity III groupnitride semiconductor crystal, a high resistivity group III nitridesemiconductor substrate, a semiconductor device and a fabrication methodof the high resistivity III group nitride semiconductor crystal (forexample, refer to Patent Document 2). In the Patent Document 2, a groupIII nitride semiconductor crystal in which Fe is doped, for example astransition metals, the group III nitride semiconductor crystal being anFe doped GaN layer whose value of the concentrations of Gallium atomvacancy is less than or equal to 1×10¹⁶ cm⁻³, is disclosed. The value ofthe concentrations of the Ferrum atoms in the Fe dope GaN layer is5×10¹⁷ cm⁻³ to 5×10²⁰ cm⁻³. Moreover, it is disclosed also about asemiconductor device, which has a semiconductor layer formed on thegroup III nitride semiconductor substrate composed of theabove-mentioned Fe dope GaN layer.

Moreover, it is already disclosed also about a semiconductor elementwhich can perform multilayer formation of a plurality of nitride basedcompound semiconductor layers, which have a difference of a latticeconstant more than a predetermined value, in the effective crystallinestate, and can control propagation of penetration dislocation to anepitaxial growth direction (for example, refer to Patent Document 3).However, in the Patent Document 3, it is not disclosed about Fe dope GaNlayer for obtaining the high resistivity group III nitride semiconductorcrystal.

-   Patent Document 1:

Japanese Patent Application Laying-Open Publication No. 2002-141499(Pages 3 to 4 and FIG. 1)

-   Patent Document 2:

Japanese Patent Application Laying-Open Publication No. 2007-184379(Pages 6 to 7, FIG. 4 and FIG. 5)

-   Patent Document 3:

Japanese Patent Application Laying-Open Publication No. 2007-221001(FIG. 1, FIG. 7, and FIG. 10)

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a semiconductor devicecomprises: a substrate; a nitride based compound semiconductor layerplaced on the substrate and doped with a first transition metal atom; analuminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1)placed on the nitride based compound semiconductor layer; a nitridebased compound semiconductor layer placed on the aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) and doped with thesecond transition metal atom; an aluminum gallium nitride layer(Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) placed on the nitride based compoundsemiconductor layer doped with the second transition metal atom; and agate electrode, a source electrode, and a drain electrode which areplaced on the aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where0.1<=y<=1).

According to another aspect of the present invention, a semiconductordevice comprises: a substrate; a nitride based compound semiconductorlayer placed on the substrate and doped with a first transition metalatom; an aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) placed on the nitride based compound semiconductor layer; anitride based compound semiconductor layer placed on the aluminumgallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) and doped witha second transition metal atom; a non-doped nitride based compoundsemiconductor layer placed on the nitride based compound semiconductorlayer doped with the second transition metal atom; an aluminum galliumnitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) placed on thenon-doped nitride based compound semiconductor layer; and a gateelectrode, a source electrode, and a drain electrode which are placed onthe aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1).

According to another aspect of the present invention, a semiconductordevice comprises: a substrate; a layered structure in which athree-layered structure is formed repeatedly multiple times, thethree-layered structure being composed of a nitride based compoundsemiconductor layer placed on the substrate and doped with a firsttransition metal atom, an aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) placed on the nitride based compoundsemiconductor layer, and a nitride based compound semiconductor layerplaced on the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) and doped with a second transition metal atom; an aluminumgallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) placed on thelayered structure; and a gate electrode, a source electrode, and a drainelectrode which are placed on the aluminum gallium nitride layer(Al_(y)Ga_(1−y)N) (where 0.1<=y<=1).

According to another aspect of the present invention, a semiconductordevice comprises: a substrate; a layered structure in which afour-layered structure is formed repeatedly multiple times, thefour-layered structure is composed of a nitride based compoundsemiconductor layer placed on the substrate, a nitride based compoundsemiconductor layer placed on the nitride based compound semiconductorlayer and doped with a first transition metal atom, an aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) placed on the nitridebased compound semiconductor layer which doped with the first transitionmetal atom, and a nitride based compound semiconductor layer placed onthe aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1)and doped with a second transition metal atom; a non-doped nitride basedcompound semiconductor layer placed on the layered structure; analuminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1)placed on the non-doped nitride based compound semiconductor layer; anda gate electrode, a source electrode, and a drain electrode which areplaced on the aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where0.1<=y<=1).

According to another aspect of the present invention, a fabricationmethod of a semiconductor device comprises: forming a nitride basedcompound semiconductor layer doped with a first transition metal atom,on a substrate; forming an aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) on the nitride based compoundsemiconductor layer; forming a nitride based compound semiconductorlayer doped with a second transition metal atom, on the aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1); forming a non-dopednitride based compound semiconductor layer on the nitride based compoundsemiconductor layer doped with the second transition metal atom; formingan aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) onthe non-doped nitride based compound semiconductor layer; and forming agate electrode, a source electrode, and a drain electrode, on thealuminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1).

According to the present invention, piezo charge can be inactivated,high frequency characteristics can be improved by obtaining a highresistivity semiconductor layer, and a highly efficient semiconductordevice and a fabrication method of the semiconductor device can beprovided, by impurity doping the transition metal atom in the galliumnitride (GaN) layer which sandwiches the upper and lower sides of theAlGaN layer or the AlN layer.

Moreover, according to the present invention, a crystal defect of theGaN layer is reduced, an amount of leakage current and an amount ofcurrent collapse can be reduced, and a semiconductor device of stablehigh frequency performance and a fabrication method of the semiconductordevice can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic section structure chart showing a semiconductordevice according to a conventional example.

FIG. 2 is a schematic section structure chart showing a semiconductordevice according to a first embodiment of the present invention.

FIG. 3 is a schematic section structure chart showing a semiconductordevice according to a second embodiment of the present invention.

FIG. 4 is a schematic section structure chart showing a semiconductordevice according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments of the present invention will be described withreference to the accompanying drawings. It is to be noted that the sameor similar reference numerals are applied to the same or similar partsand elements throughout the drawings, and the description of the same orsimilar parts and elements will be omitted or simplified. Generally, andas is conventional in the representation of the circuit blocks, it willbe appreciated that the various drawings are not drawn to scale from onefigure to another nor inside a given figure, and in particular that thecircuit diagrams are arbitrarily drawn for facilitating the reading ofthe drawings. In the following descriptions, numerous specific detailsare set forth such as specific signal values, etc. to provide a thoroughunderstanding of the present invention. However, it will be obvious tothose skilled in the art that the present invention may be practicedwithout such specific details. In other instances, circuits well-knownhave been shown in block diagram form in order to not obscure thepresent invention with unnecessary detail.

The embodiments shown below exemplify an apparatus and a method that areused to implement the technical ideas according to the presentinvention, and do not limit the technical ideas according to the presentinvention to those that appear below. These technical ideas, accordingto the present invention, may receive a variety of modifications thatfall within the claims.

[First Embodiment]

(Device Structure)

As shown in FIG. 2, a semiconductor device according to a firstembodiment of the present invention includes: a substrate 10; a nitridebased compound semiconductor layer 14 which is placed on the substrate10 and is doped with a first transition metal atom; an aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 placed on thenitride based compound semiconductor layer 14 doped with the firsttransition metal atom; a nitride based compound semiconductor layer 18which is placed on the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N)(where 0.1<=x<=1) 16, and is doped with a second transition metal atom;an aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22placed on the nitride based compound semiconductor layer 18 doped withthe second transition metal atom; and a gate electrode 26, a sourceelectrode 24, and a drain electrode 28 which are placed on the aluminumgallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22.

A two-dimensional electron gas layer 13 is formed in an interface of thenitride based compound semiconductor layer 14 doped with the firsttransition metal atom, and the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 placed on the nitride basedcompound semiconductor layer 14 doped with the first transition metalatom.

Similarly, a two-dimensional electron gas layer 17 is formed in aninterface of the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) 16 and the nitride based compound semiconductor layer 18which is placed on the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N)(where 0.1<=x<=1) 16 and is doped with the second transition metal atom.

Furthermore, a two-dimensional electron gas layer 21 is formed in aninterface of the nitride based compound semiconductor layer 18 dopedwith the second transition metal atom, and the aluminum gallium nitridelayer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22 placed on the nitride basedcompound semiconductor layer 18 doped with the second transition metalatom.

The substrate 10 can be composed of a silicon carbide (SiC) substrate, asemi insulating silicon substrate, and a sapphire substrate, etc.

The nitride based compound semiconductor layer 14 and the nitride basedcompound semiconductor layer 18 are formed, for example, by a GaN layer.

The gate electrode 26 can be formed, for example, by Ni/Au, and thesource electrode 24 and the drain electrode 28 can formed, for example,by Ti/Au.

The first transition metal atom and the second transition metal atom areone or two or more transition metal atoms, which are selected from agroup composed of ferrum (Fe), titanium (Ti), vanadium (V), chromium(Cr), manganese (Mn), cobalt (Co), nickel (Ni), and copper (Cu).

In particular, when the first transition metal atom and the secondtransition metal atom are ferrum (Fe), each of the impurity dopingconcentrations of the Fe atom in the nitride based compoundsemiconductor layer 14 and the nitride based compound semiconductorlayer 18 is more than 1×10⁷ cm⁻³. Preferably, the impurity dopingconcentrations of the Fe atom are more than 7×10¹⁷ cm⁻³. It is becausethe nitride based compound semiconductor layer 14 and the nitride basedcompound semiconductor layer 18 can be securely made semi-insulatingthrough impurity doping of the Fe atom more than 7×10¹⁷ cm⁻³.

According to the semiconductor device according to the first embodimentof the present invention, the piezo charge can be inactivated and thehigh resistivity GaN layers 14 and 18 can be obtained by impurity dopingthe transition metal atom in the GaN layer 14 and the GaN layer 18 whichsandwich the upper and lower sides of the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16.

As a result, an amount of leakage current between the gate electrode 26and the source electrode 24 or between the gate electrode 26 and thedrain electrode 28 can be reduced.

Moreover, the two-dimensional electron gas layer 17 is made toelectrically ground state in high frequency region by GaN layer 18 beinghigh resistivity layer, and a capacitor is formed between thetwo-dimensional electron gas layers 17 and 21 by inserting the GaN layer18. The value of the parasitic capacitance is also reduced and the highfrequency characteristic of the semiconductor device also furtherimproves by performing the value of the thickness of the GaN layer 18,for example more than a predetermined value of about 1 micrometer.

Moreover, a capacitor is formed between the two-dimensional electron gaslayer 13 and the SiC substrate 10 by inserting the GaN layer 14 betweenthe two-dimensional electron gas layer 13 and the SiC substrate 10, andthe two-dimensional electron gas layer 13 is made to electrically groundstate in high frequency region with the two-dimensional electron gaslayer 17 and the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) 16, by the GaN layer 14 being high resistivity layer.

As a result, the value of the parasitic capacitance is also reduced andthe high frequency characteristic of the semiconductor device alsofurther improves.

Moreover, according to the first embodiment of the present invention,the semiconductor device of stable high frequency performance, whichreduces the crystal defect of the GaN layer, reduces the amount ofleakage current and reduces the amount of current collapse, and improvesthe power amplification gain, can be provided.

[Second Embodiment]

(Device Structure)

As shown in FIG. 3, a semiconductor device according to a secondembodiment of the present invention includes: a substrate 10; a nitridebased compound semiconductor layer 12 which is placed on the substrate10; a nitride based compound semiconductor layer 14 which is placed onthe nitride based compound semiconductor layer 12 and is doped with afirst transition metal atom; an aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 which is placed on the nitridebased compound semiconductor layer 14 doped with the first transitionmetal atom; a nitride based compound semiconductor layer 18 which isplaced on the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) 16, and is doped with a second transition metal atom; anon-doped nitride based compound semiconductor layer 20 placed on thenitride based compound semiconductor layer 18 doped with the secondtransition metal atom; an aluminum gallium nitride layer(Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22 placed on the non-doped nitridebased compound semiconductor layer 20; and a gate electrode 26, a sourceelectrode 24, and a drain electrode 28 which are placed on the aluminumgallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22.

An electric charge induced by piezo polarization effect can beinactivated by intervening the nitride based compound semiconductorlayer 14 doped with the first transition metal atom between the nitridebased compound semiconductor layer 12 and the aluminum gallium nitridelayer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16. As a result, an interfacebetween the nitride based compound semiconductor layer 12 and thealuminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16can be high resistivity layer, and an amount of generating leakagecurrent can be suppressed.

Similarly, an electric charge induced by piezo polarization effect canbe inactivated by intervening the nitride based compound semiconductorlayer 18, doped with the second transition metal atom, between thenon-doped nitride based compound semiconductor layer 20 and the aluminumgallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16. As aresult, an interface between the non-doped nitride based compoundsemiconductor layer 20 and the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 can be high resistivity layer,and an amount of generating leakage current can be suppressed.

Although the two-dimensional electron gas layer 21 is formed in theinterface between the non-doped nitride based compound semiconductorlayer 20 and the aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where0.1<=y<=1) 22 placed on the non-doped nitride based compoundsemiconductor layer 20 as well as FIG. 2, the showing in the figure isomitted in FIG. 3.

The substrate 10 can be composed of a silicon carbide (SiC) substrate, asemi insulating silicon substrate, and a sapphire substrate, etc.

The nitride based compound semiconductor layer 12, the nitride basedcompound semiconductor layer 14 doped with the first transition metalatom, the nitride based compound semiconductor layer 18 doped with thesecond transition metal atom, and the non-doped nitride based compoundsemiconductor layer 20 are formed, for example, by a GaN layer.

The gate electrode 26 can be formed, for example, by Ni/Au, and thesource electrode 24 and the drain electrode 28 can formed, for example,by Ti/Au.

The first transition metal atom and the second transition metal atom areone or two or more transition metal atoms which are selected from agroup composed of ferrum (Fe), titanium (Ti), vanadium (V), chromium(Cr), manganese (Mn), cobalt (Co), nickel (Ni), and copper (Cu).

In particular, when the first transition metal atom and the secondtransition metal atom are ferrum (Fe), each of the impurity dopingconcentrations of the Fe atom in the nitride based compoundsemiconductor layer 14 and the nitride based compound semiconductorlayer 18 is more than 1×10¹⁷ cm⁻³.

(Fabrication Method)

A fabrication method of the semiconductor device according to the secondembodiment of the present invention includes the step of: forming thenitride based compound semiconductor layer 14 doped with the firsttransition metal atom on the substrate 10; forming the aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 on the nitridebased compound semiconductor layer 14; forming the nitride basedcompound semiconductor layer 18 doped with the second transition metalatom on the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) 16; forming the non-doped nitride based compoundsemiconductor layer 20 on the nitride based compound semiconductor layer18 doped with the second transition metal atom; forming the aluminumgallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22 on thenon-doped nitride based compound semiconductor layer 20; and

forming the gate electrode 26, the source electrode 24, and the drainelectrode 28 on the aluminum gallium nitride layer (Al_(y)Ga_(1−y)N)(where 0.1<=y<=1) 22.

In the following, the fabrication method of the semiconductor deviceaccording to the second embodiment of the present invention will beexplained.

-   (a) Flow TMG (trimethylgallium) and ammonia gas on the SiC substrate    10, and form the GaN layer 12, for example, in a thickness of about    1 micrometer by epitaxial growth.-   (b) Next, form GaN layer 14, for example, in a thickness of about    0.1 micrometer with epitaxial growth, by using same gas series. In    this case, Fe is doped by using ferrocene (Cp₂Fe:    bis(cyclopentadienyl)ferrum) or (HCL) Fe.-   (c) Next, flow TMAl (trimethyl aluminum) and ammonia gas, and then    form the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where    0.1<=x<=1) 16, for example, in a thickness of about 20 nm to about    100 nm by epitaxial growth.-   (d) Next, form the GaN layer 18 doped with Fe, for example, in a    thickness of about 0.1 micrometer, by epitaxial growth as well as    processing (b) as described above.-   (e) Next, flow TMG (trimethylgallium) and ammonia gas, and then form    the GaN layer 20, for example, in a thickness of about 1 micrometer    by epitaxial growth as well as processing (a) as described above.-   (f) Finally, form the aluminum gallium nitride layer    (Al_(0.3)Ga_(1−0.3)N) (where 0.1<=y<=1) 22 of about 30% of a rate of    Al composition ratio in a thickness of about 20 nm by epitaxial    growth.-   (g) Next, make vacuum evaporation of Ti/Al etc. to the source    electrode 24 and the drain electrode 28, and then form an ohmic    electrode.-   (h) Next, make vacuum evaporation of Ni/Au etc. to the gate    electrode 26, and then form a Schottky electrode.

According to the process of the above (a) to (h), the semiconductordevice according to the second embodiment of the present invention iscompleted. As the planar structure, a multi-finger type high powersemiconductor device can also be formed, for example.

According to the semiconductor device according to the second embodimentof the present invention, piezo charge can be inactivated and highresistivity GaN layers 14 and 18 can be obtained, by impurity doping thetransition metal atom in the GaN layer 14 and the GaN layer 18 whichsandwich the upper and lower sides of the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16.

As a result, an amount of leakage current between the gate electrode 26and the source electrode 24 or between the gate electrode 26 and thedrain electrode 28 can be reduced.

Moreover, a capacitor is formed in the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 and the aluminum gallium nitridelayer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22 inserting the GaN layer 20by the GaN layer 18 being high resistivity layer. The value of theparasitic capacitance is also reduced and the high frequencycharacteristic of the semiconductor device also further improves byperforming thickness of GaN layer 20, for example, more than apredetermined value of about 1 micrometer.

Moreover, a capacitor is formed between the aluminum gallium nitridelayer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 and SiC substrate 10inserting the GaN layer 12 by the GaN layer 14 being high resistivitylayer. The value of the parasitic capacitance is also reduced and thehigh frequency characteristic of the semiconductor device also furtherimproves by performing thickness of GaN layer 12, for example, more thana predetermined value of about 1 micrometer.

Moreover, according to the second embodiment of the present invention,the semiconductor device of stable high frequency performance, whichreduces the crystal defect of the GaN layer, reduces the amount ofleakage current and the amount of current collapse and improves thepower amplification gain, and the fabrication method of thesemiconductor device can be provided.

[Third Embodiment]

(Device Structure)

A semiconductor device according to the third embodiment of the presentinvention includes the layered structure (14, 16, 18) in which thethree-layered structure shown in FIG. 2 is formed repeatedly multipletimes. The three-layered structure is composed of the nitride basedcompound semiconductor layer 14 doped with the first transition metalatom, the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) 16 placed on the nitride based compound semiconductor layer14, and the nitride based compound semiconductor layer 18 placed on thealuminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16and doped with the second transition metal atom.

That is, the semiconductor device according to the third embodiment ofthe present invention includes: the substrate 10; the layered structure(14, 16, 18) which is placed on the substrate 10 and in which thethree-layered structure is formed repeatedly multiple times (forexample, about 2 to 3 times); the aluminum gallium nitride layer(Al_(y)Ga_(1−y)N) (where 0.1<=y<=1) 22 placed on the layered structure(14, 16, 18); and the gate electrode 26, the source electrode 24, andthe drain electrode 28 which are placed on the aluminum gallium nitridelayer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1). The three-tiered structure iscomposed of the nitride based compound semiconductor layer 14 doped withthe first transition metal atom, the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 placed on the nitride basedcompound semiconductor layer 14 doped with the first transition metalatom, and the nitride based compound semiconductor layer 18 placed onthe aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1)16 and doped with the second transition metal atom.

Since the detail of each layer is the same as the first embodiment,description is omitted.

Modified Example of the Third Embodiment

Furthermore, as shown in FIG. 4, a semiconductor device according to amodified example of the third embodiment of the present inventionincludes: a substrate 10; layered structures (12/14/16/18, 20/30/32/34,36/38/40/42) in which four-layered structure is formed repeatedlymultiple times (for example, about 2 to 3 times); a non-doped nitridebased compound semiconductor layer 44 placed on the layered structures;an aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 22placed on the non-doped nitride based compound semiconductor layer 44;and a gate electrode 26, a source electrode 24, and a drain electrode 28which are placed on the aluminum gallium nitride layer (Al_(y)Ga_(1−y)N)(where 0.1<=y<=1) 22. The four-layered structure is composed of anitride based compound semiconductor layer 12 placed on the substrate10, a nitride based compound semiconductor layer 14 placed on thenitride based compound semiconductor layer 12 and doped with the firsttransition metal atom, an aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16 placed on the nitride basedcompound semiconductor layer 14 doped with the first transition metalatom, and a nitride based compound semiconductor layer 18 placed on thealuminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) 16and doped with the second transition metal atom.

The first transition metal atom and the second transition metal atom areone or two or more transition metal atoms, which are selected from agroup composed of ferrum (Fe), titanium (Ti), vanadium (V), chromium(Cr), manganese (Mn), cobalt (Co), nickel (Ni), and copper (Cu).

When the first transition metal atom and the second transition metalatom are ferrum (Fe), each of the impurity doping concentrations of thenitride based compound semiconductor layer (14, 30, 38) and the nitridebased compound semiconductor layer (18, 34, 42) is more than 1×10¹⁷cm⁻³.

Since the detail of each layer is the same as the second embodiment,description is omitted.

According to the semiconductor device according to the third embodimentand the modified example of the third embodiment of the presentinvention, crystal quality can be improved according to the dislocationsuppressing effect in LOG (Lateral OverGrowth) of the aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1), by forming thelayered structure in which the layered structure composed of the nitridebased compound semiconductor layer placed at the upper and lower sidesof the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where0.1<=x<=1) and doped with the transition metal atom is formed repeatedlymultiple times.

According to the third embodiment and the modified example of the thirdembodiment of the present invention, piezo charge can be inactivated,and high frequency characteristics can be improved by obtaining a highresistivity semiconductor layer, and also crystal quality can beimproved by laminated layered-structure, and a highly efficientsemiconductor device can be provided, by impurity doping with thetransition metal atom in the gallium nitride (GaN) layer whichsandwiches the upper and lower sides of the AlGaN layer or the AlNlayer.

Moreover, according to the present invention, the amount of crystaldefects of the GaN layer can be reduced, and the amount of leakagecurrent and the amount of current collapse can be reduced, and alsocrystal quality can be improved by laminated layered-structure, and asemiconductor device of stable high frequency performance can beprovided.

Other Embodiments

While the present invention is described in accordance with theaforementioned embodiments, it should not be understood that thedescription and drawings that configure part of this disclosure are tolimit the present invention. This disclosure makes clear a variety ofalternative embodiments, working examples, and operational techniquesfor those skilled in the art.

In addition, it cannot be overemphasized that the amplifying elementsare applicable not only to FET but also other amplifying elements, suchas HEMT (High Electron Mobility Transistor), LDMOS FET (Lateral DopedMetal-Oxide-Semiconductor Field Effect Transistor) and HBT(Hetero-junction Bipolar Transistor).

The substrate region may be provided with either a SiC substrate, a GaNsubstrate, a substrate in which a GaN epitaxial layer is formed on a SiCsubstrate, a substrate in which a GaN epitaxial layer is formed on an Sisubstrate, a substrate in which a heterojunction epitaxial layercomposed of GaN/GaAlN is formed on a SiC substrate, a substrate in whicha GaN epitaxial layer is formed on a sapphire substrate, a sapphiresubstrate or a diamond substrate.

Accordingly, the technical scope of the present invention is defined bythe claims that appear appropriate from the above explanation, as wellas by the spirit of the invention. Various modifications will becomepossible for those skilled in the art after receiving the teachings ofthe present disclosure without departing from the scope thereof.

Industrial Applicability

According to the present invention, a semiconductor device is appliedfor the semiconductor device with a SiC substrate or a GaN substrate andhas a wide range of application fields, such as an internally matchedpower amplifier, a power MMIC (Monolithic Microwave Integrated Circuit),a microwave power amplifier, and a millimeter-wave power amplifier.

1. A semiconductor device comprising: a substrate; a first nitride basedcompound semiconductor layer placed on the substrate and doped with afirst transition metal atom; an aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) placed on the first nitride basedcompound semiconductor layer; a second nitride based compoundsemiconductor layer placed on the aluminum gallium nitride layer(Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) and doped with a second transitionmetal atom; an aluminum gallium nitride layer (Al_(y)Ga_(1−y)N) (where0.1<=y<=1) placed on the second nitride based compound semiconductorlayer doped with the second transition metal atom; a gate electrode, asource electrode, and a drain electrode which are placed on the aluminumgallium nitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1); a firsttwo-dimensional electron gas layer formed in an interface of the firstnitride based compound semiconductor layer and the aluminum galliumnitride layer (Al_(x)Ga_(1−x)N) where 0.1<=x<=1); a secondtwo-dimensional electron gas layer formed in an interface of thealuminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) andthe second nitride based compound semiconductor layer; and a thirdtwo-dimensional electron gas layer formed in an interface of the secondnitride based compound semiconductor layer and the aluminum galliumnitride layer (Al_(y)Ga_(1−y)N) (where 0.1<=y<=1), wherein a layeredstructure in which a multi-layered structure is formed, themulti-layered structure being composed of the first nitride basedcompound semiconductor layer doped with the first transition metal atom,the aluminum gallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1)placed on the first nitride based compound semiconductor layer, and thefirst nitride based compound semiconductor layer placed on the aluminumgallium nitride layer (Al_(x)Ga_(1−x)N) (where 0.1<=x<=1) and doped withthe second transition metal atom, and wherein the first transition metalatom and the second transition metal atom are ferrum (Fe) and the firstnitride based compound semiconductor layer and the second nitride basedcompound semiconductor layer are made semi-insulating through impuritydoping of the ferrum (Fe) atom more than 7×10¹⁷ cm⁻³, each of athickness of the first nitride based compound semiconductor layer andthe second nitride based compound semiconductor layer is more than 1micrometer, the second two-dimensional electron gas layer is made toelectrically ground state in high frequency operational region of thesemiconductor device through a capacitor formed between the secondtwo-dimensional electron gas layer and the third two-dimensionalelectron gas layer by the second nitride based compound semiconductorlayer being made insulating, and the first two-dimensional electron gaslayer is made to electrically ground state in high frequency operationalregion of the semiconductor device through a capacitor formed betweenthe first two-dimensional electron gas layer and the substrate by thefirst nitride based compound semiconductor layer being made insulating.